Researchers at the Changchun Institute of Optics, Fine Mechanics and Physics of the Chinese Academy of Sciences uncovered a new energy transfer mechanism that significantly enhances the red emission in upconversion systems. The study was published in The Journal of Physical Chemistry Letters. Upconversion systems are key to technologies in display devices, solar cells, and bioimaging, where materials absorb low-energy near-infrared (NIR) light and re-emit it as visible light. In the case of Er3+/Yb3+ co-doped systems, the typical upconversion luminescence produces green and red emissions, with the red emission being of particular interest. However, achieving efficient red emission has been challenging.
In this study, researchers focused on the Er3+/Yb3+ system. They discovered that a new round-trip energy transfer (RTET) process dominates the red emission mechanism. This process operated through two distinct steps, an energy transfer from Er3+ to Yb3+, and a reverse energy transfer that excited Er3+ from a lower state to a red-emitting state. This RTET mechanism enhances the intensity of red emission and significantly alters the temporal dynamics of the emitted light.
Moreover, researchers demonstrated that RTET enhances the red-to-green emission ratio (R/G) across various Yb3+ concentrations. With the increase in Yb3+ content, the RTET mechanism became more dominant, reaching efficiencies exceeding 90% for Yb3+ concentrations of 10% or more. This resulted in faster red emission, with the decay time of the red light becoming similar to that of the green light, showcasing the efficiency of the RTET process.
These findings provide a deep understanding of how RTET influences the color and temporal behavior of upconversion luminescence in the Er3+/Yb3+system. The efficiency of RTET is particularly beneficial for devices that rely on high-quality red emission, such as lasers, light-emitting diodes (LEDs), and photovoltaic systems.
Also, this study provides insights into how the concentration of Yb3+ ions can be tuned to optimize the red emission. This ability to fine-tune emission properties is key for developing more efficient materials for smart windows, displays, and even medical imaging devices.
The authors suggest that further exploration into the interaction dynamics between Er3+ and Yb3+ ions will lead to greater enhancements in luminescence properties.
